The present invention relates to a method for characterizing defects on silicon surfaces, in particular silicon wafers, a method for treating silicon surfaces with an etching solution and the etching solution to be employed in the method and process of the present invention.
Crystalline defects in substrate for microelectronic devices are highly undesirable as they have a negative impact on the functionality and reliability of integrated circuits, formed using the substrates, such as wafers, in particular silicon-on-insulator (SOI) type wafers. The typical approach for identifying crystalline defects and thereby characterizing the quality of substrate surfaces is the use of so-called structural etching solutions. These etching solutions, due to the dependency of the etch rate from crystalline structures, can identify crystalline defects, since crystalline defects give rise to either hillocks or etch pits after application of the structural etching solution.
Various etching solutions have been proposed for silicon surfaces which require typically the presence of strong oxidants.
W. C. Dash in the Journal of Applied Physics, vol. 27, no. 10, pp. 1193-1195 (1956) discloses a further etched solution able to reveal defects on semiconductor substrates, consisting of hydrofluoric acid, nitric acid and acetic acid. While this solution is able to etch semiconductor substrates, including silicon substrates, the etching solution according to Dash is not able to differentiate between different types of defects and furthermore does not provide a satisfactory etch rate.
U.S. Pat. No. 2,619,414 discloses a further chemical etchant to be applied on semiconductor surfaces to improve their electrical characteristics. The chemical etchant disclosed in that patent comprises acetic acid, nitric acid, hydrofluoric acid and bromine. The drawback of the composition of that patent is the use of bromine, which is highly instable and volatile, so that the chemical etchant according to this prior art reference can only be stored for a very short time in the dark at low temperatures and can be handled only under ventilation, since bromine evaporates from the composition. Although bromine is not as toxic as chromate or dichromate, precautionary measures nevertheless have to be taken when using that chemical as an etchant.
In view of the progress in semiconductor industry, involving in particular the decrease of the minimum feature sizes used to fabricate integrated circuits, the introduction of new substrate materials, such as silicon-on-insulator (SOI) or strained-silicon-on-insulator (sSOI), improved methods for quality characterization are required, in particular with respect to the following features:
Satisfactory etch rates, so that even thin substrates can be etched with sufficient control of etch rate/etch time/removed surface thickness.
Etch sensitivity, i.e. the possibility to detect different types of defects (such as D defects corresponding to agglomerates of vacancies and oxygen precipitates), most preferably identifying different types of defects after one type of etching treatment.
Reduction of health risks and environmental problems by using suitable components for the etching composition, without sacrificing the desired properties, etch rate, etch sensitivity etc.
Stability of the etching composition, so that same can be stored for a certain period of time and can be handled without highly elaborated safety measures.
Thus, there is a need for improved etching compositions and etching processes for such purposes and these are now provided by the present invention.